Fluid pressure motor construction



Feb. 26, 1963 M. CRIPE FLUID PRESSURE MOTOR CONSTRUCTION Filed Jan. 29, 1959 INVEI-7TOR. MAXWELL L. CRIPE.

A TTORNE Y.

l I a i -arena @hme Patented Feb. 26, 1963 3,078,677 FLUKE PREEiSURE MOTOR CUNSTRUCTIGN lt iaxweil L. Gripe, outh fiend, ind, assignor to The Eendix tlorporation, a corporation of Delaware Filed Jan. 29, 1959, Ser. No. 789,828 ti Claims. (Cl. till-54.6)

The present invention relates to power operated master cylinders; and more particularly to an improved short stroke type or": unit.

An object of the present invention is the provision of a new and improved construction for a short stroke power operated master cylinder which does not have an objectional amount of lost motion during its actuation.

Another object of the present invention is the provision of a new and improved construction for a short stroke power operated master cylinder which is simple in its design, rugged in its construction, and which can be manufactured and assembled quickly and cheaply without introducing an appreciable amount of lost motion into the vehicles braking system.

The invention resides in certain constructions and combinations and arrangements of parts; and further objects and advantages of the invention will become apparent to those skilled in the art to which the invention relates from the following description of the preferred embodiment described with reference to the accompanying drawing forming a part of this specification and in which:

FIGURE 1 is a cross sectional view of a fluid pressure servomotor driven master cylinder for actuating the brakes of an automotive vehicle, and which embodies principles of the present invention;

FIGURE 2 is a fragmentary isometric view showing a part of the unit seen in FIGURE 1; and

FIGURE 3 is a fragmentary cross sectional view better illustrating a fastening device seen in FIGURE 1.

The fluid pressure servomotor driven master cylinder shown in the drawing is of the type used to power actuate the hydraulic braking systems of automotive vehicles. The unit shown in the drawing generally comprises a hydraulic master cylinder A having a fluid displacement member ll therein that is driven by a pair of power actuated pistons B and B of the vacuum powered fluid pressure servomotor C that is suitably bolted to one end of the hydraulic master cylinder A. Force from the pistons B and B is transmitted to the fluid displacement piston it} by means of a push rod D; and power actuation of the pistons B and B is controlled by means of valve structure E carried by the pistons and which in turn is actuated by the foot pedal lever F of the automotive vehicle.

The master cylinder A is of conventional construction wherein the fluid pressurizing chamber 12 which slidably receives the displacement piston it) is positioned in a casting 14 which also includes a reservoir cavity 16 in the region overlying the fluid pressurizing chamber 12. The fluid pressurizing chamber 12 opens into the end of the casting 14 that is bolted to the servomotor C, and the fluid displacement member is prevented from being withdrawn from the fluid pressurizing chamber 12 by means of a snap ring 1% which acts as a return stop for the displacement piston 30. The fluid displacement piston It) is provided with suitable seals 2i) and 22 adjacent its inner and outer ends respectively, and a suitable compensating port 24 is provided between the reservoir 16 and the chamber 12 in the region forwardly of the seal 2.59 when the piston 153 is adjacent to the stop 18. Fluid displaced by the piston it) flows through a suitable back pressure valve as which may be of the construction shown in application Serial No. 676,699, filed August 2, 1957, now Reissue Patent No. 24,664, and which permits fluid to be forced through suitable openings therein to the outlet port 28 to the brakes of the vehicle The back pressure valve 26 is -tion in said chamber.

urged against a shoulder 30 by a coil spring 32 to prevent flow from the chamber around the outside edges of the back pressure valve. Return flow through the outlet port 28 lifts the back pressure valve 26 from the shoulder 30 until such time as its pressure upon the valve equals the force of the coil spring 32-at which time the back pressure valve again seats to thereafter hold a predetermined slight positive pressure upon the system to which port 28 is connected.

The fluid pressure motor C shown in the drawing is formed by means of a stamped generally cylindrically cupshaped shell 34 having a centrally located flanged opening in its bottom end 38 which receives and is suitably sealed to a boss 4% of the master cylinder A through which boss its fluid pressurizing chamber 12. extends. The sidewalls of the internal power chamber of the servomotor C are generally smooth and cylindrically shaped for reasons which will later be apparent, and also are provided with a stepped down portion or shoulder 42 spaced from its outer end.

As previously indicated the servomotor C is provided with a pair of pistons B and B which pistons are spaced axially of each other in a tandem arrangement. The outer piston B is provided with an axially inwardly extending boss 44 having four fillets 46 on its outer surface at its point of puncture with the main body portion of the piston B and the piston B is provided with an axially outwardly extending annular boss 48 which telescopes over the external fillets 46 of the piston B The piston B is provided with a plurality of internal fillets 50 adjacent the inner end of its internal opening 52, which fillets 50 engage the surface of the boss 44 to space the bosses 44 and 48 apart and thereby provide a fluid flow passage therebetween. Telescopic movement of the piston B upon the piston B is prevented by abutment of the outer end of its boss 48 with the fillets 46; and separation of the pistons B and B is prevented by means of a snap ring 54 suitably carried by the inner end of the boss 44 and which is abutted by the inner face of the piston B Power pistons B and B are of the diaphragm type in which a diaphragm structure is used to effect a seal between the center rigid portion of the piston and the sidewalls of the servomotor to separate the motor into opposing fluid pressure chambers. The diaphragms 56 and 58 of the pistons B and B respectively are of a new and improved design having a pro-molded laterally (generally axially extending) turned portions 69 and 62 respectively which end in radially inwardly protruding bulges 64 and 66 respectively and by reason of which a suitable seal is effected with respect to the sidewalls of the servomotors internal chamber when the diaphragms are slid axially into posi- The laterally turned portions 60 and 62 are stretched over the opposite ends of an annular partition member 68 having a radially inwardly extending portion 76 which effects sliding seal with respect to the external surface of the annular boss 48 of the piston B The outer peripheral axially extending flange of the partition member 68 is provided with a pair of grooves 74 and 76 in its outer surface adjacent its opposite ends, and the bulges s4 and as are stretched over their respective ends of the partition member 68 to be received in the grooves 74 and '76, respectively. The clearance provided by the opposite end portions of the axially extending flange and the bottom or" their respective recesses 74 and 76 with respect to sidewalls of the servomotors internal chamber is less than the thickness of the laterally turned portions of the diaphragms 56 and 53 respectively; so that when the internal partition member 68 having the diaphragms 56 and 53 stretched thereon is inserted into the shell 34, a seal is accomplished therebetwcen. inward movement of the partition member 68 is limited by the stepped down portion 42 of the shell 34. The shoulder 42 may be made to operatively abut any portion of the partition member 68, as for example the face of the diaphragm 58; and in the preferred embodiment shown in the drawing, is so positioned as to engage a similar shoulder provided on the partition member 63 generally opposite to its radially inwardly extending portion '76.

The servomotor is assembled by placing the partition member 63 over the annular boss 48 of a piston B having a diaphragm 53 sealingly attached thereto-dollowing which the boss 44 of piston B is slipped into the annular boss 43 and locked in place with the snapped portion 54. The inner end of diaphragm 56 is positioned on the piston B and locked in place by means of valve cover plate 89, and the outer ends of the diaphragm 56 and 58 are expanded over their respective ends of the partition member 68. The composite structure so formed is then slid axially into the shell 34 until its shoulder 78 abuts the shoulder 42 to thereby squeeze the folded over portions 69 and 62 against the cylindrically shaped sidewalls of the servomotor and thereby eltect a seal therewith. The assembly is locked in place by means of a cover plate 82 whose outer peripheral edge is just received within the shell 34 and which is pressed up against the outer surface of the diaphragm 56. The cover plate 82 is in turn held in place by means of a piece of bent wire 84 which extends around the inside of the shell 34 and whose ends project out through a slot 86 adjacent the open end of the shell 34. The bent wire 84 has eight evenly spaced radially outwardly extending loop portions 88 which in the assembled position of the wire, project out matching openings 90 through the sidewalls of the shell 34. The matching openings 90 are spaced apart axiahy from the shoulder 42 at such a distance as to permit the loops of the internal wire 88 to snap into the openings 90 when the partition member 63 is in abutment with the shoulder 42 and pressure is applied to the cover plate 82 to hold it against the diaphragm 56. The portion of the diaphragm 56 that is abutted by the cover plate 82 will preferably include a plurality of evenly spaced knobs or projections which can be yieldingly compressed to accommodate the manufacturing tolerances of the parts.

As previously indicated the servomotor shown in the drawing is a tandem piston unit having an inner power piston B and outer power piston B The inner power piston B divides the space between the partition member 68 and the inner end of the servomotor shell 34 into an inner opposed fluid pressure chamber 92 positioned forwardly of the piston B and an outer opposing chamber 94 positioned between piston B and the partition member 6%. The power piston B divides the space between the partition member 68 and the outer cover plate 82 into an inner opposing power chamber 96 positioned forwardly of the piston B and an outer opposing power chamber 98 positioned rearwardly of the piston B The servomotor shown in the drawing is what is known as an atmospheric suspended unit in which the inner and outer opposing chambers for both pistons are communicated with atmospheric pressure during the normal deenergized condition of the servomotor; and in which unit, vacuum from the intake manifold of the vehicles propelling engine is communicated to both of the inner opposing power chambers 92 and 96 when the servomotor is actuated. The outer opposing chamber 94 for the piston B is continually communicated with the atmosphere through openings 100 and 102 through the partition member 68 and shell 34 respectively; and the outer opposing power chamber 93 for the piston B is continually communicated with the atmosphere through a suitable opening in the cover plate 82. Vacuum from the intake manifold of the vehicles propelling engine is communicated to the servomotor through the vacuum conduit 104 having a flexible portion 106 which coils around the inside of the servomotor and is connected to the control valve structure E that is carried by the units internal power piston structure.

The control valve structure E is formed by suitable tion of the piston 13 with a shoulder or atmospheric valve seat 122 which is valve chambers that are integrally cast in the piston B and valve cover plate and control of the unit is had by means of an axially positioned valve plunger or poppet member 198 which in turn is actuated from the brake pedal lever F of the vehicle by means of an interconnecting push rod 119.

The atmospheric valve chamber 112 is formed by means of an axially positioned cavity in the piston B and which is at all times communicated with its outer opposing power chamber 93 through a passage 114; and the vacuum valve chamber 116 is formed by an annular cavity in the valve cover plate 86 that surrounds and is separated from the poppet member 108 by an annular vacuum valve seat 118. Vacuum is continually communicated with the vacuum valve chamber 118 by the flexible vacuum conduit portion 106; and the vacuum valve chamber 116 is separated from the atmospheric valve chamber 112 by a flexible diaphragm 120, through the central opening of which the poppet member 108 extends. The portion of the diaphragm surrounding the poppet member 163 is suitably stifienecl to provide firm engagement with the vacuum valve seat 118, and the outer portion of the diaphragm 123 is sealingly clamped between the valve cover plate 80 and the main body por- Poppet member 108 is provided adapted for sealing engagement with the diaphragm 120, and which is capable of lifting the diaphragm from engagement with the vacuum valve seat 118. The annular space between the atmospheric and vacuum valve seats 122 and 113 respectively provides the valves control pressure chamber 124; and the chamber 124 is at all times communicated with the inner opposing power chamber 96 through the control passageway 126. The inner opposing power chamber 96 is in turn at all times communicated with the other inner opposing power chamber 92 through the annular clearance 128 which has previously been described as being formed between the bosses 44 and 43 of the pistons B and B respectively. The atmospheric valve seat 122 is normally held out of engagement with the diaphragm 120 by means of a valve return spring 139 that is interpositioned between a washer 132 attached to the poppet member 108 by means of a snap ring 134 and the other end of which operatively abuts the inner end of the atmospheric valve chamber 112 to communicate atmospheric pressure to the chambers 92 and 96.

in order that the units will be provided with reaction means for apprising the operator of the amount of force which is being delivered to the master cylinder A, the push rod D is provided with a plunger 136 that is slidingly received within a bore 133 in the inner end of the boss 44. The inner end of the poppet member 108 is received in a smaller diameter bore 149 that communicates with the bore and a rubber disk 142 is positioned between the bottom of the bore 138 and the plunger 136, so that it will be resiliently squeezed into engagement with the inner end of the poppet member 168 when the piston structure exerts force against the plunger 36. During no power conditions, the inner end of the poppet member 1 .33 will be forced directly into engagement with the rubber disk 142 to thereby manually actuate hydraulic piston it). In order that the plunger 136 will not be forced out of its bore 133, a washer 14s of Z-shaped cross section is interpositioned between the washer 132 and the power piston structure so that the washer 132 will engage the Z-shaped washer 144- before the plunger 136 is moved out of the bore 138. A rubber washer 1 .6 is positioned between the Z-shaped washer 144 and the piston structure B to prevent audible clicking noises.

The power operated master cylinder shown in the drawing is a comparatively short stroke unit in which the fluid displacement member 1% will have a maximum stroke of approximately 1% inches. The foot pedal lever P which actuates the unit is provided with a mechanical advantage of approximately 3; so that any lost motion produced by the stack up of manufacturing tolerances, very noticeably affects the feel and the performance of the unit. As previously indicated, compensation between the fluid displacement chamber 12 and the reservoir 16 is accomplished by means of an interconnecting port 24 which is sealed off when the forward piston seal 20 is slid forwardly over its opening in the sidewalls of the chamber 12. The fluid that is within the chamber 12 cannot be pressurized, therefore, until the forward lip of the seal 2i! has been slipped forwardly over the port 24; and it will, therefore, be seen, that any forward motion of the piston '19 prior to the time that the port 24 is closed off, does no useful Work-and what is more, is reflected in considerable annoying play in the foot pedal lever F.

in order that the unit shown in the drawing can be manufactured by conventional production machinery and still provide an acceptable, satisfactory feeling and operating unit, suitable and inexpensive means are provided which permits the seal 2% to be quickly and accurately located with respect to the port 24. The structure cornprises a generally cup-shaped stamping 148 having rolled threads on its outer circumference, which in turn engage threads that are rolled on the inside of an axially outwardly extending flange portion 159 that is stamped on the units cover plate 82. The inner end of the cupshaped stamping 148 is rolled over to provide an abutment flange 152, and a rubber valve rod 154 that is positioned over the push rod 119 with its outer periphery interpositioned between the flange 152 and the valve cover plate 250 to provide a resilient bumper. In order that the cup-shaped stamping 148 can be axially positioned quickly during the assembly operation, its sidewalls are provided with four holes 156 therethrough--any one of which may be aligned with a corresponding opening 158 through the sidewalls of the flange 150. .A coiled wire spring 16%) is provided with a radially inwardly extending leg 162, so that the wire can be snapped around the outside of the flange portion 150 with its leg 162 projecting into the opening 158. Once the cup-shaped stamping 148 is approximately positioned and the leg 162 is inserted into the opening 158, rotation of something less than 90 of the cup-shaped stamping 143 will align one of its holes 156 with the opening 158; whereupon the leg 162 will snap through the aligned hole 156 to lock the cup-shaped stamping .148 in place. Prior to the time that the coil spring 166 is installed upon the flange 150, the assembler looks through the opening provided for the filler cap 164 for the reservoir 16 to observe whether or not the lip of the seal 20 is covering the compensating port 24. In some instances a wire might be inserted into port 24 to tell whether or not the seal 20 has cleared the port. In the preferred method of assembly, the cover plates 32 will come to the assembler with their cupshaped stampings 148 projecting a considerable distance axially inwardly. When so assembled, the seal 21) will be observed to close off the port 24; and after the assembler backs the cup-shaped stamping 148 off with respect to the cover plate 82 to the point where the lip of the seal 20 is seen to move past the center of the port 24, the spring 1% is placed into position as previously described. Thereafter the cup-shaped stamping 143 is further backed off until the leg r152 snaps into its locking position. The outer end of the cup-shaped stamping 14% is provided with a generally square opening 166 to receive a specially made annular adjusting tool which slips over the push rod 116 and fits into the square opening 166 to rotate the stamp ing 14%.

The pistons B and B are normally held into engagement with the cup-shaped stamping 148 by means of the coil spring 32 and the power piston return spring 168 that is positioned between the piston B and the inner end of the shell 34. Operation of the unit shown in the drawing is initiated by depressing the foot pedal lever P; whereupon the atmospheric valve seat 122 is moved out of the position shown in the drawing into engagement with the valves diaphragm 129 to close off further communi- 6. cation of the atmospheric valve chamber 112 with the valves control chamber 124 and hence with the inner opposing power chambers 96 and d2. Further inwardv movement of the poppet member 1% causes the atmospheric valve seat 12?. to lift the diaphragm 126 out of engagement with the vacuum valve seat 118 and thereby introduce vacuum to the inner opposing power chambers 96 and 92. As previously indicated atmospheric pressure is continually communicated to the outer opposing power chambers 4 and @S, and the introduction of vacuum to the inner opposing power chambers 92 and 96 causes the pistons B and B to move forwardly to thereby drive the piston 1% into the fluid pressurizing chamber 12 to displace fluid therefrom. Initial movement of the piston it] causes its seal 2% to close off the compensating port 24; whereupon further inward movement of the piston 1t displaces fluid past the residual pressure check valve 26 in a manner which will be understood by those skilled in the art. I

A predetermined clearance is provided between the inner end of the poppet member 103 and the rubber disk 142 to permit the above described valve actuating movement to occur without the poppet member 198 abutting the rubber disk 142. Continued inward movement of the poppet member 198 holds the diaphragm 125! out of engagement with the vacuum valve seat 113 causing increasing diiferential pressure to be established across the pistons B and 13 so that they follow the inward movement of the poppet member 1%. When the inward movement of the poppet member 1% is stopped, the pistons B and B move inwardly slightly thereafter to bring the vacuum valve seat 118 into sealing engagement with the diaphragm 129; whereupon further inward movement of the pistons B and B ceases. During inward movement of the pistons B and B increasing amounts of force are transmitted to the plunger 136 causing the rubber disk 142 to be deformed against the poppet member 1ii8-thereby producing a reaction against the foot pedal lever P which will be generally proportional to the amount of force being developed by the servomotor. Retraction of the foot pedal lever F permits the forces produced by the valve return spring 130 and the rubber disk .142 to bias the poppet member 1% rearwardly until its atmospheric valve seat 122 moves out of engagement with the diaphragm 120 to thereby communicate atmospheric pressure with the opposing power chambers and 92. The resulting decrease in differential pressure across the power pistons B and B permits the forces produced by the hydraulic fluid within the chamber 12, and that produced by the return spring 168, to move the pistons B and B rearwardly. The pistons B and B move rearwardly following the movement of the atmospheric valve seat 122. and when its movement ceases, further slight rearward movement of the pistons B and 3;, brings the diaphragm into engagement with the atmospheric valve seat 122 to lap the valve and prevent further deenergization of the scrvomotor. A complete retraction of the foot pedal lever F permits the servomotor to be completely deenergized and the pistons B and B to be biased rearwardly by the spring 168 until the rubber valve rod 154 moves into abutment with the flange 152 of the cup-shaped stamping 148.

It will be apparent that the obiects heretofore enumerated as well. as others have been accomplished; and that there has been provided a new and improved servomotor construction and method of assembling the same which can be manufactured on a mass production basis at considerably less cost than prior art structure.

While the invention has been described in considerable detail, I do not wish to be limited to the particular constructions and methods shown and described. it is my intention to cover hereby all novel adaptations, modifications and arrangements thereof which come within the practice of those skilled in the art to which the invention relates. I

I claim:

1. In a power operated master cylinder: at body memher having axially aligned fluid pressurizing and power chambers, a movable wall in said power chamber, a hydraulic piston in said fluid pressm'izin cha iber actuated by said movable wail, said fluid pressurizing chamber having a compensating port in its sidewalls, and said piston having a cup-shaped seal on its inner end which slides over and closes off said compensating por, an end wall on the end of said power chamber opposite from said fluid pressurizing chamber, said end wall having a generally centrally located axially outwardly extending annular flange with an opening therethrough, control valve structure carried by said movable wall and bovin a control portion projecting through said opening in said flange, an annular stop member having an opening therein through which said control portion of said control valve projects, said stop member being threaded in said opening in said flange for abutment by said movable wall, said stop member having means by which it may be rotated with respect to said flange for locating said stop member axially, said having a generally radially extending opening through its side which communicates with said stop member, said stop member having a plurality of generally radially extending circumferentially spaced openings th ough its side for sequential alignment with said opening in said flange during rotation in said flange, and a generally circular piece of spring wire extending around the outside of said annular to bias a radially inwardly extending portion of said wire through aligned open'ngs of said flange and stop member.

2. In 0. pr. er operated master cylinder: a body memher having axially aligned fluid prcssurizing and power chambers, a movable wall in said power chamber, a hydraulic piston in said lluid pressurizing chamber actuated by said movable well, said fluid pressurising chamber having a compensating port in its sidewalls, and said piston having a cup-shaped seal on its inner end which slides over and closes oil said compensating port, an end wall on the end of said power chamber opposite from said fluid pressurizing chamber, said end wall having a generally centrally located axially outwardly extend annular flange with an opening th rethrough, control valve structure carried by said mov ole wall and having a control portion projecting througl said opening in said flange, an annular generally cup-shaped stop member threaded in said opening in said for abutment by said movable wall, stop member having a generally square axially extending opening therethrough through which said control portion of said valve extends and by means of which it may be rotated with respect to said flange for lo ng said stop axially, said flange having a generally rad lly extending opening through its side which communicates with said stop member, said stop member having a plurality of generally radially extending circumferer. 'ally spaced openings through its side for sequential alignment with said opening in said flange, and a generally circular piece of spring wire extending around the or "isle of said annular flange biasing radially inwardly extending portion of said spring wire through aligi ed openings of said and stop member.

3 I a motor: a body member having a generally axially mending power chamber with opposite end walls therein, a movable wall in said power chamber adapted for axial movement between said end i ills, said movable wall having a normal position adjacent one of said end walls, said one end wall having a generally centrally located axially outwardly extending annular flange with an opening thcrcthrough, control valve structure carried by said movable wall and having a contro portion projecting through said opening in said flange, an annular stop member having an opening therein through which said control portion or" said control valve projects, said stop member being threaded in said opening in said flange and having means by which it may be rotatcd with respect to said flange for locating said stop member axially, said flange having a generally radially extending opening through its side which communicates with said stop member, said stop member having a plurality of generally radially extending circumferentially spaced openings through its side for sequential alignment with said openin in said flange, and a generally circular piece of spring wire extending around the outside of said annular flange biasing a radially inwardly extending portion of said spring wire through aligned openings of said flange and stop member.

4. In a power operated master cylinder: 2: body memher having axially aligned fluid pressurizing and power chambers, a movable wall in said power chamber, fluid displacement means in said fluid pressurizing chamber actuated by said movable wall, fluid compensating valve means in the sidewalls of said fluid pressurizing chamber and actuated by said fluid displacing means, said compensating valve means being opened by movement of said fluid displacement means toward said power chamber and being closed when said fluid displacement means is moved to a predetermined position in said fluid pressurizing chamer, an end wall on the end of said power chamber oppo site from said fluid pressnrizing chamber, said end Wall having a generally centrally located axially outwardly extending flange with an opening therethrough, control valve structure carried by said movable wall and having a control portion projecting through said opening in said flange, and an annular stop member having an opening therein through which said central portion of said control portion projects, said stop member being threaded in said opening in said flange for abutment by said movable wall, said stop member having means by which it may be rotated with respect thereto to position said stop member in and out of said flange, said fiangc having a generally radially extending opening through its side which communicates with said stop member, said stop member having a plurality of generally radially extending circumferentially Spaced openings through its side for sequential alignment with said opening in said fian e during rotation, and a generally circular piece of spring wire extending around the outside of said annular flange to bias a radially inwardly extending portion of said spring wire through aligned openinvs of said flange and stop member.

5. In a power operated master cylinder; at body memher having aligned fiuid pressurizing and power chambers with said fluid prcssurizing chamber being positioned forwardly of said power chamber, a movable wall in said power chamber, a hydraulic piston in said fluid pressurizing chamber operatively abutted by said movable wall for forward motion, compensating means for said fluid prcssurizing chamber, said hydraulic piston having a gcnorally normal retracted pos on relative to said cornpensating means, means closing said compensating means when said hydraulic piston is moved forwardly of said generally normal retracted position and opening said compensating means when said hydraulic piston is moved rearwardiy into said retracted position, said power chamber having a rear end wall rearwardly of said movable wall, valve means carried by said movable wall and having a control member projecting rearwardly through said rear end Wall, and an adjustable stop mounted on said rear end wall for abutting said movable wall to adjust the amount of forward movement that is required to close said compensating means.

6. in a power operated master cylinder; 2. body member having aligned fluid pressurizing and power chambers with said fluid pressurizing chamber being positioned forwardly of said power chamber, a movable wall in said power chamber, a hydraulic piston in said fluid pressurizing chamber operatively abutted by said movable wall for forward motion, compensating means for said fluid pressurizing chamber, said hydraulic piston having a generally normal retracted position relative to said compensating means, means closing said compensating means when said hydraulic piston is moved forwardly of said generally normal retracted position and opening said compensating means when said hydraulic piston is moved rearwardly into said retracted position, said power chamber having a rear end wall rearwardly of said movable wall, valve means carried by said movable wall and 5 having a control member projecting rearwardly through said rear end wall, and an annular adjustable stop mounted on said rear end wall surrounding said control member for abutting said movable wall to adjust the amount of forward movement that is required to close 10 said compensating means.

Osborn May 16, 1922 15 10 Trail Oct. 9, Duty et al June 24, Stelzer Mar. 10, Ingres Apr. 24, Phillips Aug. 28, Ingres Feb. 19, Rockwell Aug. 31, Schultz Oct. 16, Anderson Jan. 1, Wurtz et al. Mar. 31,

FOREIGN PATENTS France May 28, Great Britain June 9,

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,078,677 February 26, 1963 Maxwell L. Cripe tified that error appears in the above r xumbered pat- It is hereby oer hat the said Letters Patent should read as ent requiring correction and t corrected below.

Column 2, line 26, for "puncture" read juncture Signed and sealed this 24th day of December 1963.

(SEAL) EDWIN L, REYNOLDS Attest:

ERNEST W. SWIDER I Attesting Officer A t ng Commissioner of Patents 

1. IN A POWER OPERATED MASTER CYLINDER: A BODY MEMBER HAVING AXIALLY ALIGNED FLUID PRESSURIZING AND POWER CHAMBERS, A MOVABLE WALL IN SAID POWER CHAMBER, A HYDRAULIC PISTON IN SAID FLUID PRESSURIZING CHAMBER ACTUATED BY SAID MOVABLE WALL, SAID FLUID PRESSURIZING CHAMBER HAVING A COMPENSATING PORT IN ITS SIDEWALLS, AND SAID PISTON HAVING A CUP-SHAPED SEAL ON ITS INNER END WHICH SLIDES OVER AND CLOSES OFF SAID COMPENSATING PORT, AN END WALL ON THE END OF SAID POWER CHAMBER OPPOSITE FROM SAID FLUID PRESSURIZING CHAMBER SAID END WALL HAVING A GENERALLY CENTRALLY LOCATED AXIALLY OUTWARDLY EXTENDING ANNULAR FLANGE WITH AN OPENING THERETHROUGH, CONTROL VALVE STRUCTURE CARRIED BY SAID MOVABLE WALL AND HAVING A CONTROL PORTION PROJECTING THROUGH SAID OPENING IN SAID FLANGE, AN ANNULAR STOP MEMBER, HAVING AN OPENING THEREIN THROUGH WHICH SAID CONTROL PORTION OF SAID CONTROL VALVE PROJECTS, SAID STOP MEMBER BEING THREADED IN SAID OPENING IN SAID FLANGE FOR ABUTMENT BY SAID MOVABLE WALL, SAID STOP MEMBER HAVING MEANS BY WHICH IT MAY BE ROTATED WITH RESPECT TO SAID FLANGE FOR LOCATING SAID STOP MEMBER AXIALLY, SAID FLANGE HAVING A GENERALLY RADIALLY EXTENDING OPENING THROUGH ITS SIDE WHICH COMMUNICATES WITH SAID STOP MEMBER, SAID STOP MEMBER HAVING A PLURALITY OF GENERALLY RADIALLY EXTENDING CIRCUMFERENTIAL SPACED OPENINGS THROUGH ITS SIDE FOR SEQUENTIAL ALIGNMENT WITH SAID OPENING IN SAID FLANGE DURING ROTATION IN SAID FLANGE, AND A GENERALLY CIRCULAR PIECE OF SPRING WIRE EXTENDING AROUND THE OUTSIDE OF SAID ANNULAR FLANGE TO BIAS A RADIALLY INWARDLY EXTENDING PORTION OF SAID WIRE THROUGH ALIGNED OPENINGS OF SAID FLANGE AND STOP MEMBER. 